This invention generally relates to a navigation system that is environmentally controlled for temperature, pressure, and/or vibration and shock. More specifically, the invention relates to a borehole navigation system that is environmentally controlled for temperature, pressure, and/or drilling vibration.
For several reasons, it is essential for a drill pipe operator to accurately monitor and guide the direction of the drill bit such that a borehole is created where desired. One reason is that it is expensive to drill a borehole at a cost of about $500,000 per day. Another reason is that it may be necessary by law for an oil rig to log the location of its boreholes at a regular frequency such that the oil rig can be properly monitored. However, the high temperature, pressure, shock, vibration, and size constraints during drilling a borehole can make it difficult for equipment to properly monitor the location of the borehole. Current systems may only achieve a borehole accuracy of about 60 feet for every 25,000 feet drilled, which is not sufficient for some applications.
To determine the location of a termination in a borehole, it is desirable to know the termination""s azimuth and vertical orientation. Typically, gyroscopes can be used to determine the azimuth. However, gyroscopes typically do not function adequately in the high temperatures and pressures associated with high depth boreholes. Consequently, gyroscopes typically have not found much commercial acceptance in these applications.
Many prior art systems have attempted to accurately and efficiently monitor the location of the drill bit to determine its location, but each system has had limitations. In one prior art system, the drill bit was removed from the borehole and a monitoring tool was lowered down the borehole to determine its current location. A disadvantage of this system is that it is costly to stop drilling and spend time removing the drill bit to take measurements with the monitoring tool.
In another prior art system, single-axis accelerometers have been used to determine the vertical location of the drill bit. A system such as this, however, does not provide the azimuth of the drill bit, which is necessary to determine the full location of a borehole: a system that uses a single accelerometer is typically only adequate if the oil rig is going to drill a vertical borehole.
In yet other prior art systems, a magnetometer is used to determine the magnetic field direction from which the azimuth is approximated. However, systems such as these must make corrections for magnetic interference and use of non-magnetic drill pipe. Additionally, systems that rely only on magnetometers to determine the azimuth can suffer accuracy degradation due to the earth""s changing magnetic field.
It is therefore an object of this invention to provide an environmentally mitigated navigation system that effectively controls the temperature of an inertial measurement unit within an isolating chamber.
It is a further object of this invention to provide such an environmentally mitigated navigation system that can be placed within a drill pipe and lowered into a borehole at great depths.
It is a further object of this invention to provide such an environmentally mitigated navigation system that does not have to be removed from a drilling borehole for inertial measurements to be taken.
It is a further object of this invention to provide an environmentally mitigated navigation system that can control the temperature of the inertial measurement unit at a time when it is not being powered.
This invention results from the realization that, for an environmentally mitigated navigation system, the temperature of an inertial measurement unit can be effectively controlled by a temperature control system that includes a thermoelectric cooling system which when powered cools and maintains the temperature of the inertial measurement unit and a phase change device for maintaining stable temperature window for the inertial measurement unit when the temperature control system is not being powered by an external power device. In another embodiment of the invention, the temperature control system only includes a thermoelectric cooling system that is used while the drilling mud driver provides electric power to the temperature control system.
The invention further features an environmentally mitigated navigation system including a drilling mud driver electric generator, a thermal and pressure isolating chamber, and an inertial measurement unit, for making inertial measurements, that is disposed on the isolating chamber, a temperature control system, and a vibration and shock isolation system for reducing vibration of the inertial measurements at least during drilling periods. The temperature control system includes a thermoelectric cooling system powered by the drilling mud driver for maintaining the inertial measurement unit at a predetermined temperature in a powered mode and a phase change device for maintaining the inertial measurement unit at substantially the predetermined temperature in an unpowered mode while the phase change device changes states to define a stable temperature window for the inertial measurement unit to make inertial measurements during the unpowered mode.
The invention features an environmentally mitigated navigation system that includes a thermal isolating chamber, an inertial measurement unit for making inertial measurements, and a temperature control system. The temperature control system includes a thermoelectric cooling system, which in a powered mode maintains the inertial measurement unit at a substantially predetermined temperature, and a phase change device for maintaining the inertial measurement unit at substantially a predetermined temperature in an unpowered mode. The phase change device substantially maintains the predetermined temperature by changing phase to define a stable temperature window for the inertial measurement unit to make inertial measurements during the unpowered mode.
In a preferred embodiment of the invention, the thermal isolating chamber may be pressure resistant. The inertial measurement unit may include a microelectromechanical sensor (MEMS). The inertial measurement unit may include at least one gyroscope and at least one accelerometer for determining the azimuth and the vertical orientation, respectively, of the inertial measurement unit. The inertial measurement unit may include three gyroscope input axes and three accelerometer input axes. Additionally, the inertial measurement unit may include one or more gimbals for determining one or more measurement biases of the inertial measurement unit. The thermoelectric cooling system may include semiconductor devices. The phase change device may include a medium that changes from solid to liquid near the operating temperature. The medium of the phase change device may be, for example, paraffin. The environmentally mitigated navigation system may include a drilling mud driver electric generator for powering the thermoelectric system in a powered mode. The environmentally mitigated navigation system may also include an isolation system for reducing the vibration and shock of the inertial measurement unit such that inertial measurement can be effectively made.
The invention also features an environmentally mitigated borehole navigation system including a drilling mud driver electric generator, a thermal and pressure isolating chamber, an inertial measurement unit, for making inertial measurements, which is disposed in the isolating chamber, a temperature control system, and a vibration and shock isolation system. The temperature control system includes a thermoelectric cooling system powered by the drilling mud driver electric generator for maintaining the inertial measurement unit at a predetermined temperature. The vibration and shock isolation system reduces the vibration to which the inertial measurement unit is exposed at least during drilling periods.
In a preferred embodiment, the inertial measurement unit may include microelectromechanical system (MEMS). The environmentally mitigated borehole navigation system may include at least one gyroscope and at least one accelerometer for determining the azimuth and the vertical orientation, respectively, of the inertial measurement unit. The inertial measurement unit may include three gyroscopes and three accelerometers. The inertial measurement unit may include one or more gimbals for determining one or more measurement biases of the inertial measurement unit. The thermoelectric cooling system may include a semi-conductor device. The temperature control system may further include a phase change device for maintaining the inertial measurement unit at substantially the predetermined temperature when the thermoelectric cooling system is unpowered and a medium of the phase change device is changing phase. The medium of the phase change device may change phase from solid to liquid near the operating temperature. The medium of the phase change device may be, for example, paraffin.